Thickness shear mode quartz resonator sensors have been used successfully in the downhole environment of oil and gas wells for several decades and are an accurate means of determining downhole pressures in widespread use in hydrocarbon (e.g., oil and gas) exploration and production, as well as in other downhole applications. Quartz resonator pressure sensors typically have a crystal resonator located inside a housing exposed to ambient bottomhole fluid pressure and temperature. Electrodes on the resonator element coupled to a high frequency power source drive the resonator and result in shear deformation of the crystal resonator. The electrodes also detect the resonator response to pressure and temperature and are electrically coupled to conductors extending to associated power and processing electronics isolated from the ambient environment. Ambient pressure and temperature are transmitted to the resonator, via a substantially incompressible fluid within the housing, and changes in the resonator frequency response are sensed and used to determine the pressure and/or temperature and interpret changes in same. For example, a quartz resonator sensor, as disclosed in U.S. Pat. Nos. 3,561,832 and 3,617,780, includes a cylindrical design with the resonator formed in a unitary fashion in a single piece of quartz. End caps of quartz are attached to close the structure.
Generally, a pressure transducer comprising a thickness shear mode quartz resonator sensor assembly may include a first sensor in the form of a primarily pressure sensitive thickness shear mode quartz crystal resonator exposed to ambient pressure and temperature, a second sensor in the form of a temperature sensitive quartz crystal resonator exposed only to ambient temperature, a third reference crystal in the form of quartz crystal resonator exposed only to ambient temperature, and supporting electronics. The first sensor changes frequency in response to changes in applied external pressure and temperature with a major response component being related to pressure changes, while the output frequency of the second sensor is used to temperature compensate temperature-induced frequency excursions in the first sensor. The reference crystal, if used, generates a reference signal, which is only slightly temperature-dependent, against or relative to which the pressure-induced and temperature-induced frequency changes in the first sensor and the temperature-induced frequency changes in the second sensor can be compared. Such comparison may be achieved by, for example, frequency mixing frequency signals and using the reference frequency to count the signals from the first and second sensors for frequency measurement.
Prior art devices of the type referenced above including one or more thickness shear mode quartz resonator sensors exhibit a high degree of accuracy even when implemented in an environment such as a downhole environment exhibiting high pressures and temperatures. However, when implemented as pressure sensors, the sensors in these devices must be at least partially exposed to the exterior environment surrounding the device. For example, when implemented in a downhole environment, the sensors may be exposed to pressures up to about 30,000 psi (about 206.84 MPa) and temperatures of up to 200° C. Accordingly, in order to comply with such extreme pressure and temperature environments and shifts in pressure and temperature, the housings of such devices enclosing the sensors must be designed and manufactured to be substantially robust as to not fail when implemented in the field exposed to such pressures and temperatures.
For example, where pressure transducers are required to at least partially expose one or more pressure sensors within the pressure transducer to the pressure of the external environment (e.g., via a fluid within the sensor), the housing of the transducer must be designed to enable the pressure sensors to be in communication with pressure of the external environment while still maintaining structural integrity and protecting other components of the transducer, such as, for example, reference sensors, temperature sensors, and other electronics in the transducer from the surrounding extreme pressure and temperature environments. In some implementations, it is required to pass connections, such as electrical conductors, along the length of the transducer and past the pressure sensors from one component to another component within or external to the transducer. Thus, passing the electrical conductors past each pressure sensor may be difficult as such connections must be routed through or around portions of one or more pressure housings having the pressure sensors therein and that are equipped to handle the forces from pressures and temperatures of a downhole environment.